Control method for high-quality DC (direct current)/AC (alternating current) converter of grid-connected photovoltaic power system

Abstract

The invention provides a control method for a high-quality DC (direct current) / AC (alternating current) converter of a grid-connected photovoltaic power system, belongs to the grid-connected photovoltaic power technology, and aims to develop a high-quality DC / AC converter suitable for grid-connected operation. The control method is characterized in that a phase-shifting transformer grid connection mode is adopted, current distribution and control are performed on three-phase bridge inverters (3 and 4) according to specific conversion laws of the formula (1) and the formula (2), thyristor controllability is realized, a multi-level synthetic technology adopting equal-increment step-shaped triangular-wave current waveform is adopted, a current waveform similar to a sine wave is obtained at an output side of the phase-shifting transformer, the functions of low harmonic control, lead-lag continuous adjustment of a power factor and free regulation of direct current in the range ranging from 0 to a rated value are realized, and the method is applied to grid-connected photovoltaic power systems with various capacities.

Description

technical field [0001] The invention belongs to photovoltaic power grid-connected technology. Background technique [0002] One of the core technologies of photovoltaic power generation grid-connected system is DC / AC converter, usually called inverter. When the first photovoltaic power generation device came out in the 1980s, it used thyristor inverters, but since the 1990s, photovoltaic inverters have all used fully-controlled switching devices. Applied research on inverters has disappeared from scientific publications. [0003] The main switching devices of inverters in the current grid-connected photovoltaic power generation system use power field effect transistors (MOSFETs), insulated gate bipolar transistors (IGBTs), gate turn-off thyristors (GTOs), and gate commutation Thyristor (IGCT), etc., the control method adopts pulse width modulation (PWM), etc., and the topology adopts voltage source inverter and current source inverter. [0004] At present, the types of sm...

AI Technical Summary

Problems solved by technology

[0004] At present, the types of small-scale photovoltaic converters less than 6kW are relatively complicated. They are basically single-phase systems without a transformer structure. There are problems such as DC current injection, leakage current generated by common-mode voltage, and large harmonics to varying degrees, so it is difficult to connect to the grid.

The construction methods of 6-100kW medium-sized photovoltaic converters also have diversified characteristics. There are both single-phase systems and three-phase systems, or three-phase systems combined with single-phase systems; there are both transformer-less structures and transformer output systems; The system without a transformer structure also has the same problem as the small photovoltaic converter, and also has the problem of difficulty in connecting to the network; although the system output through the transformer does not have the problem of network isolation, there are problems of efficiency and harmonics

[0007] To sum up, the existing grid-connected converters for photovoltaic power generation have problems to varying degrees. With the rapid development of photovoltaic power generation technology and the wide application of photovoltaic power generation, technical solutions to improve grid-connected converters for photovoltaic power generation are also emerging, but No innovative research results have been seen so far

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